1. Field of the Invention
The present invention relates to a developing device, an image forming apparatus, and a toner detection method.
2. Description of the Related Art
A conventional electrographic image forming apparatus configured to supply toner from a toner container to a developing unit has to control the amount of toner to be supplied from the toner container to the developing unit. Remaining toner amount detection control is known in which, in order to control the amount of toner supply, a light transmission type sensor that detects the amount of toner in the developing unit is provided and, from the light transmission amount, the amount of toner remaining in the developing unit is measured.
In the remaining toner amount detection control where the light transmission type sensor is provided, a stirring paddle is provided on the optical path and the stirring paddle stirs the toner in the developing unit when remaining amount detection is performed. A configuration is known in which light is periodically blocked to clean the transparent members on the surfaces of the light emitting element and the light receiving element of the light transmission type sensor at a given cycle with a cleaning member that is provided on the stirring paddle.
In the above-descried configuration, light detection/non-detection by the light receiving element periodically changes because the light is blocked periodically. Regarding the light detection/non-detection, when an amount of remaining toner is large, the time during which no light is detected is long. On the other hand, when an amount of remaining toner is small, the time during which the light is detected is long. The control is known in which the amount of remaining toner is determined according to this time difference.
A means has been disclosed that, in order for accurate detection of the amount of toner remaining in a developing unit, includes a cleaning member that cleans a transmission window in a remaining amount detection method using a light transmission type sensor and determines an amount of remaining toner when the time during which a light receiving element of the light transmission type sensor detects light exceeds a given time (see, Japanese Laid-open Patent Publication No. 06-149055).
However, in the above-descried conventional configuration for detecting the amount of remaining toner using the light transmission type sensor and the cleaning member, the time during which the light receiving element detects or does not detect light varies depending on the flowability of the toner to be detected. In other words, in a state where toner is on the optical path, the cleaning member cleans the surface of the element and accordingly the toner on the optical path is raked out so that the optical path transmits light. The raked-out toner then goes back to the optical path again depending on its flowability so that light is blocked. If the toner has good flowability, because the toner goes back to the optical path soon after being raked out, the period during which light is transmitted shortens. On the other hand, if the toner has poor flowability, because the toner does not go back soon after being raked out, the period during which light is transmitted gets longer.
There is a problem that, because the toner flowability varies depending on the degree of deterioration of the toner and changes of the temperature and humidity, if such a change occurs, the amount of toner remaining in the developer cannot be detected accurately.
In view of the above circumstances, there is a need to implement accurate detection of the amount of toner remaining in the developing device.